title: Characterization of the purified pituitary cytosolic NADPH:5 alpha-dihydroprogesterone 3 alpha-hydroxysteroid oxidoreductase.
abstract: The purified cytosolic 3 alpha-hydroxysteroid oxidoreductase (3 alpha-HSOR) from female rat pituitary which catalyzes the reversible conversion of 5 alpha-dihydroprogesterone (5 alpha-DHP) to 3 alpha, 5 alpha-tetrahydroprogesterone (3 alpha, 5 alpha-THP) has been characterized in terms of its steroid substrate specificity, dihydrodiol dehydrogenase activity and inhibition by drugs such as medroxyprogesterone and indomethacin. The purified enzyme has a strong preference for the C21 progestin steroid substrates, 5 alpha-DHP and 3 alpha, 5 alpha-THP, over the corresponding C19 androgenic steroid substrates, 5 alpha-dihydrotesterone (5 alpha-DHT) and 3 alpha, 5 alpha-tetrahydrotestosterone (3 alpha, 5 alpha-THT). The apparent Km for 5 alpha-DHP (80 nM) is about 250 times lower than the Km for the androgenic steroid, 5 alpha-DHT (21 microM). In the oxidative direction, the apparent Km for 3 alpha, 5 alpha-TP (1.4 microM) is about 3-fold lower than the Km for the androgenic steroid, 3 alpha, 5 alpha-THT (4.2 microM). A number of other naturally occurring 3-keto- and 3 alpha(beta)-hydroxy-steroids were assessed for their ability to act as inhibitors (alternate substrates) of the 3 alpha-reduction of 5 alpha-DHP catalyzed by the purified 3 alpha-HSOR. None of the 3 beta- or 5 beta-isomers had any effect. Of the other 3-keto and 3 alpha- steroids tested, only deoxycorticosterone and the ovarian progestins showed any significant inhibition. These may be acting as inhibitors since there was little, if any, direct 3 alpha-reduction of progesterone to 3 alpha-hydroxy-4-pregnen-20-one. Unlike the liver cytosolic 3 alpha-HSOR, the pituitary enzyme has no associated dihydrodiol (quinone) dehydrogenase activity. This enzyme is similar to other cytosolic 3 alpha-HSORs from liver and brain in that it is potentially inhibited by indomethacin and by medroxyprogesterone.
authors.affiliation: Department of Physiological Chemistry, University of Wisconsin-Madison 53706.
authors.forename: J S
authors.initials: JS
authors.lastname: Campbell
authors.forename: H J
authors.initials: HJ
authors.lastname: Karavolas
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D045002:3-alpha-Hydroxysteroid Dehydrogenase (B-Specific); D043582:5-alpha-Dihydroprogesterone; D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D005260:Female; D007213:Indomethacin / Q000494:pharmacology; D008525:Medroxyprogesterone / Q000494:pharmacology; D008623:Mercaptoethanol / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology*; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010902:Pituitary Gland / Q000201:enzymology*; D011277:Pregnanediones / Q000378:metabolism*; D011280:Pregnanolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity
chemical_list: D011277:Pregnanediones; D011374:Progesterone; D009249:NADP; D008623:Mercaptoethanol; D043582:5-alpha-Dihydroprogesterone; D011280:Pregnanolone; D010088:Oxidoreductases; D015096:3-Hydroxysteroid Dehydrogenases; D000429:Alcohol Oxidoreductases; C023125:dihydrodiol dehydrogenases; D045002:3-alpha-Hydroxysteroid Dehydrogenase (B-Specific); D044925:Oxidoreductases Acting on CH-CH Group Donors; C116788:cis-1,2-dihydro-1,2-dihydroxynaphthalene dehydrogenase; D008525:Medroxyprogesterone; D007213:Indomethacin